A large number of compounds have been proposed as antibiotics produced by microorganisms and having an antitumor activity. However, they generally have strong toxicity to normal cells or do not necessarily exhibit excellent effectiveness against solid cancers.
Chrysomycins and their related compounds are known as antibiotics having an antitumor activity and low toxicity (for example, U. Weiss et al., The Journal of Antibiotics, Vol. 35, 1982, 1194-1199). In the course of investigations on antibacteriophage active substances, chrysomycins were found as antibiotics produced by Streptomyces sp. A-419 and having an in vivo antitumor activity against P388 lymphocytic leukemia in mice.
However, there still remains a need for the provision of a compound having low toxicity and exhibiting remarkable effectiveness against solid cancers. Accordingly, an object of the present invention is to provide compounds which, as compared with well-known compounds, have low toxicity and more excellent efficacy against solid cancers in particular.